The moment you believe the phone is going to be seized by law enforcement and you act accordingly to make it more difficult or impossible to retrieve data from it, you are guilty of spoliation / tampering of evidence. This is the same set of laws that makes it illegal to shred papers before law enforcement can get to them. Locking or erasing your phone is simply the digital equivalent.

Couldn't you also apply this argument to everything? The client turned on full disk encryption 5 years before this arrest because he wanted to make it difficult for anybody (including law enforcement) to read the content of the disk.

I think you could just argue that you didn't want the disturbed and/or wanted to save some battery.

> Couldn't you also apply this argument to everything? The client turned on full disk encryption 5 years before this arrest because he wanted to make it difficult for anybody (including law enforcement) to read the content of the disk.

No. The difference is that the action is taken to obstruct a specific investigation. Generally protecting information without regard to a specific investigation is not obstruction. Same as shredding papers years before they become relevant to an investigation is also not obstruction.

> I think you could just argue that you didn't want the disturbed and/or wanted to save some battery.

Like perjury, proving obstruction may be difficult. That doesn't make it any less illegal.

"I just turned it off since the battery wears down really quickly and I thought I might need it to make a call later."

Difficult to prove.

Difficult to prove and illegal. Like lots of things.

Since when is turning off your phone illegal?

Any muppet attorney can come up with a hundred reasons why this was a perfectly reasonable thing to do.

Illegal to turn off the phone before the TSA checkpoint?